1. Field of the Invention
The present invention relates to a process for manufacturing a small-sized electric circuit for firing a pyrotechnical device.
The invention also relates to the electric circuit obtained more especially by the above-mentioned process.
2. Description of the Prior Art
Known electric firing devices comprise an electric circuit which comprises an electrically resistant element which heats or is melted under the effect of the passage of an electric current applied to the terminus of the circuit so as to cause deflagration of the explosive which is in contact with this resistant element.
Such devices are used more especially for firing munitions used in weapons with tubes such as rapid firing guns (3,000 shots per minute or more).
In these firing devices, the electric circuit is formed by a miniaturized printed circuit comprising a very fine electrically resistant wire having a diameter equal to about ten microns which is soldered to this printed circuit.
Soldering of this electrically resistant wire to the printed circuit is a very delicate and costly operation.
In addition, the circuits thus formed are relatively unreliable. In fact, in such a circuit, the probability of firing must be zero below a given electric voltage applied to the filament and must be equal to unity in a well defined time for a voltage greater than the above mentioned value. It can be readily understood that, if there exists the slightest soldering defect of the filament and if the defect has dimensions or a section deviating however little from the optimum values, the firing may be obtained in some cases at a much lower voltage and in other cases at a voltage higher than the desired optimum value.
From the French Pat. No. 2,013,677 a process is known for manufacturing an electric circuit comprising an electrically resistant element for firing a pyrotechnic device. This process comprises the steps in which a sheet of electrically resistant material is fixed to an electrically insulating support, two conducting zones separated by an electrically resistant element are etched on this sheet and each of these two conducting zones is covered at least partially by a layer of a conducting material providing electrical contact with the terminals feeding the electric current to the circuit.
This document provides no precise details of how to obtain reliable operation of the circuit obtained.
The aim of the present invention is to overcome the disadvantages of known electric circuits by proposing a process for manufacturing a circuit for firing a pyrotechnic device which is both simple and economic to construct and allows a circuit to be obtained whose operation is much more reliable than in the case of known construction.